1. Field of the Invention
The present invention relates to a machine tool for machining a workpiece into a desired shape by a tool by moving at least one of the workpiece and the tool with the workpiece rotated around a predetermined axis, and also relates to a control method for the same.
2. Description of the Related Art
A numerically controlled machine tool is conventionally known. As shown in JP-A-4-51301, the machine reads a machining program block by block and executes the operation as defined by each block.
An electronic-cam-controlled machine tool is also conventionally known as a replacement of a conventional mechanical-cam-controlled machine tool. As shown in JP-A-3-296109, a driving control apparatus of a machine tool comprises a pulse encoder mounted on a rotatable member, storage means for storing an ever-changing rotational position by reading a pulse signal from the pulse encoder, and another storage means for storing a command position data of a moving axis set for every unit rotational position of the rotatable member. Such driving control apparatus generates an ever-changing moving command data for the moving axis according to the stored rotational position data and the stored command position data. It also generates a command speed data for the moving axis in synchronous with the rotational speed of the rotatable member according to the generated moving command data and the stored rotational position data, thereby controlling the position of a tool based on the generated moving command data and the generated command speed data.
The numerical control is based on time while the electronic cam control is based on a rotation of a spindle (workpiece). If the numerical control and the electronic cam control coexist in machining of a workpiece, the machining accuracy is deteriorated because the movement of the workpiece and/or the tool under the numerical control cannot be executed in synchronous with those under the electronic cam control.
An object of the present invention is to provide a machine tool and a control method therefor where machining accuracy of the workpiece by the tool is improved even when the numerical control and the electronic cam control coexist.
The present invention provides a machine tool for machining a workpiece into a desired shape by a tool by moving at least one of the workpiece and the tool with the workpiece rotated around a predetermined axis, comprising:
reference clock signal generating means for generating a clock signal at a predetermined interval;
workpiece rotation control means for controlling the workpiece to rotate at a desired rotational speed on the basis of the clock signal generated at the reference clock signal generating means;
pulse signal generating means for generating a pulse signal every predetermined rotational angle of the predetermined axis;
first moving position determining means for determining the moving position of at least one of the workpiece and the tool at a predetermined rotational angle position of the workpiece in response to the pulse signal;
first moving control means for controlling the movement, of at least one of the workpiece and the tool in response to the pulse signal so that at least one of the workpiece and the tool may be moved to the moving position determined by the first moving position determining means;
divided timing signal generating means for generating a divided timing signal every predetermined time interval on the basis of the clock signal generated at the reference clock signal generating means;
second moving position determining means for determining the moving position of at least one of the workpiece and the tool for the every predetermined time interval; and,
second moving control means for controlling the movement of at least one of the workpiece and the tool in response to the divided timing signal so that at least one of the workpiece and the tool may be moved to the moving position determined by the second moving position determining means
The present invention also provides a control method for a machine tool for machining a workpiece into a desired shape by a tool by moving at least one of the workpiece and the tool with the workpiece rotated around a predetermined axis, the machine tool comprising:
reference clock signal generating means for generating a clock signal at a predetermined interval;
pulse signal generating means for generating a pulse signal every predetermined rotational angle of the predetermined axis; and,
divided timing signal generating means for generating a divided timing signal every predetermined time interval on the basis of the clock signal generated at the reference clock signal generating means;
the control method comprising:
controlling the workpiece by workpiece rotation control means to rotate at a desired rotational speed on the basis of the clock signal generated at the reference clock signal generating means;
determining the moving position of at least one of the workpiece and the tool at a predetermined rotational angle position of the workpiece in response to the pulse signal by first moving position determining means;
controlling the movement of at least one of the workpiece and the tool in response to the pulse signal by first moving control means so that at least one of the workpiece and the tool may be moved to the moving position determined by the first moving position determining means;
determining the moving position of at least one of the workpiece and the tool for the every predetermined time interval by second moving position determining means; and,
controlling the movement of at least one of the workpiece and the tool in response to the divided timing signal by second moving control means so that at least one of the workpiece and the tool may be moved to the moving position determined by the second moving position determining means.
According to the machine tool or the control method of the present invention, the movement of at least one of the workpiece and the tool is executed under electronic cam control in response to a pulse signal from the pulse signal generating means. Particularly, at least one of the workpiece and the tool is moved to a moving position, which is a position determined by the first moving position determining means, by the first moving control means while the workpiece is rotated at a desired rotational speed on the basis of a clock signal from the reference clock signal generating means. Therefore, the movement of at least one of the workpiece and the tool by the first moving control means is controlled in synchronous with a clock signal from the reference clock signal generating means.
According to the machine tool or the control method for the same of the present invention, the movement of at least one of the workpiece and the tool is executed under numerical control in response to a divided timing signal from the divided timing signal generating means. Particularly, at least one of the workpiece and the tool is moved to a moving position, which is a position determined by the second moving position determining means, by the second moving control means while the divided timing signal is generated at a predetermined time interval on the basis of a clock signal from the reference clock signal generating means. Therefore, the movement of at least one of the workpiece and the tool by the second moving control means is also controlled in synchronous with a clock signal from the reference clock signal generating means.
In the present invention having the above described features, the movement of at least one of the workpiece and the tool by the first moving control means is adapted to be in synchronous with the movement of at least one of the workpiece and the tool by the second moving control means, thereby enabling an improvement of machining accuracy even when a numerical control and an electronic cam control coexist.